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Pilot study Anoxia method 2008


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The objective of this pilot study was to detect whether CO2- enriched high expansion foam has the potential to be an acceptable and efficient method for emergency killing of poultry. When we take into account behavioural parameters, measurements of heart rate and pathological data, it is our conclusion that CO2 foam is a potentially acceptable killing method for laying hens.

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Pilot study Anoxia method 2008

  1. 1. 285© 2008 Universities Federation for Animal WelfareThe Old School, Brewhouse Hill, Wheathampstead,Hertfordshire AL4 8AN, UKAnimal Welfare 2008, 17: 285-288ISSN 0962-7286A pilot study to assess whether high expansion CO2-enriched foam isacceptable for on-farm emergency killing of poultryMA Gerritzen*†and J Sparrey‡†Animal Sciences Group WUR, Department of Animal husbandry, Division Animal Welfare & Health, PO Box 65, 8200 AB Lelystad,The Netherlands‡Livetec, 1 Sand Road, Flitton, Bedford MK45 5DT, UK* Contact for correspondence and requests for reprints: marien.gerritzen@wur.nlAbstractThis pilot experiment was conducted to ascertain whether CO2-enriched high expansion foam could be an acceptable and efficientalternative in emergency killing of poultry. This method could have wide-ranging applications but with particular emphasis on small(backyard) flocks, free-range sheds or open (naturally-ventilated) housings. The objectives of the study were as follows: 1) todetermine whether the injection of foam and being covered with foam leads to fear or panic reactions in birds; 2) to determine thetime taken to render birds unconscious and dead and 3) to determine whether any pathological abnormalities are observedpost mortem. Six laying hens were individually exposed to increasing levels of CO2foam with an expansion rate of 300:1. The testbox containing individual birds filled with foam within 30 s. During foaming, two out of six birds tried to escape from the test box(1–2 attempts per bird). Apart from displaying greater alertness, birds showed no aversive reactions to the CO2foam. Twenty-to-thirty seconds after being covered with foam, five of the six birds demonstrated one or two forcable or convulsive movements.Movement patterns and muscle jerks immediately following this convulsive movement led us to believe that birds lost consciousnessat this moment and, within approximately three minutes, all birds had ceased to have a heartbeat. Macroscopic post mortem exam-ination of the birds revealed no abnormalities and microscopic examination showed moderate bronchiolar bleeding and a smallamount of alveolar bleeding. After assessing behavioural parameters, measurements of heart rate and pathological data, it is ourconclusion that CO2foam has the potential to be an acceptable method of killing poultry. It is advisable for this method to beexamined on a larger scale in order to assess the implications of physiological (EEG and ECG) measurements on welfare.Keywords: animal welfare, carbon dioxide, emergency killing, euthanasia, foam, poultryIntroductionOutbreaks of highly pathogenic avian influenza havenecessitated the large scale killing of poultry that haveeither contracted or been exposed to the disease. Forinstances in which this has occurred in commercial poultryflocks, one of the methods deployed is gassing the birds intheir growing sheds, thereby reducing the need forpersonnel to enter the shed and collect live, infected birds(Gerritzen et al 2004, 2006b). In Europe, this requiresdoors, ventilation openings and other small holes in shedsto be sealed up, while in the US a polythene tent isconstructed over the birds. Carbon dioxide is then intro-duced into the enclosure to kill the birds. Both methodsrequire personnel to enter the shed to seal it. An alternative,more efficient way of delivering gas to birds in a shed orcontainer has been proposed; to use gas-filled foam(Kiezebrink 2007). The potential advantages of this systemwould be that as the gas is contained in the foam, thebuilding or pen would not have to be sealed and far lesspeople would be needed to manage the operation.The use of standard firefighting foaming equipment has beentested and deployed in the United States in an attempt to reducethe number of people potentially coming into contact with thevirus. Trials of foaming systems to date (Dawson et al 2006;Benson et al 2007) have used medium (ie expansion rate infire-fighting terms is defined as the ratio of volume of liquid tothe volume of foam produced; in general, low expansion foamhas a ratio up to 20:1, medium up to 200:1 and high over 200:1)fire-fighting foam to create a blanket over the birds to restrictoxygen availability, so that the birds die of hypoxia. Thestructure and size of the foam used in these trials was such thatsmall bubbles were found in the airways of the birds. Theconclusion reached was that the foam caused an occlusion ofthe airway, meaning that birds typically expire as a result ofhypoxia. However, issues regarding animal welfare still requireto be addressed and the need to optimise and/or modify foam-killing methods is well recognised.It is suggested that two possible options exist for optimisingthe foam-killing method, maintaining the efficacy of theUniversities Federation for Animal Welfare Science in the Service of Animal Welfare
  2. 2. 286 Gerritzen and Sparreymethod while at the same time reducing the negative effectson animal welfare. The first aspect is to increase the diameterof the foam bubbles to prevent airway occlusion. The secondis to add a gas or mixture of gases to the foam to induce rapidunconsciousness prior to death. The aim of the present pilotstudy is to combine an increase in bubble size with an anaes-thetic or lethal gas. More precisely, it is intended to createconditions of hypercapnia, thereby inducing unconscious-ness that is followed by death. It was hoped that the findingsof this pilot study would determine whether CO2-enrichedfoam is an acceptable method of emergency killing inpoultry. To this end, the aims of our study were as follows:to determine whether foam injection and subsequentimmersion leads to fear or panic reactions in birds; todetermine the time taken for a high expansion foamcontaining bubbles of 100% CO2gas to render birds uncon-scious and dead and to determine whether there is foam orwater in the lungs, abnormalities (ie bleeding) in the brain orother organs and visible irritation of the eyes and or airways.Materials and methodsThe equipment that was used in the trial was supplied byLST International (Epe, The Netherlands) and creates acarbon dioxide-rich environment around the birds which isreadily inhaled, leading rapidly to unconsciousnessfollowed by death. This is achieved through generation ofhigh-expansion foam with bubbles containing 100% CO2.The size of the bubbles ensures birds are killed as a result ofexposure to the gas and not by occlusion of the airway.Ethical aspects of the experiment were judged and approvedby the animal ethical committee of the institute.FoamThe foam is based on a commercially-available fire-fightingfoam (Ajax HTF 1000, Ajax Fire Security, Amsterdam, TheNetherlands) but with a number of modifications; mostnotably the expansion rate and the levels of CO2contained inthe foam. The foam is generated by blowing high pressureCO2gas over a pre-mixed solution of 3% concentrate (2-butoxy-ethanol) through a specially-designed foam generator.In this way a high expansion (~300:1) foam is generated withbubbles (10–50 mm in diameter) filled with 100% CO2.Animals and test situationSix 50-week old laying hens were fitted with a transmitter(TA11CTA-F40, Data Science International, St Paul, Mn,USA) to measure temperature and heart rate during eachfoaming experiment. The transmitters were modified to beused externally on the animals. Two silver (55% silver,21% copper, 24% zinc) spiked electrodes (2.5 cm long andwith a diameter of 0.1 cm) were connected to the 10 cmlong transmitter leads. The electrodes were puncturedsubcutaneously on to the right and left of the chest and thetransmitter with the leads was fixed externally to the chestusing medical tape bandage. Immediately following trans-mitter attachment, animals were placed into the test boxand the signal checked. This was received by four linkedBMC receivers under the base plate of the test box.The test box (0.94 × 0.84 × 0.80 m; length × width × height)was constructed of four wire mesh side walls, a Perspexfloor and four removable Perspex side plates at the insideof the wire mesh cage. A digital camcorder was placedabove the test box for recording birds’ behavioural parame-ters. The camera covered the entire test area.During foaming, CO2concentration was measured using aCO2Guardian Measurement Unit (PBI, Dansensor,Ringsted, Denmark) with a range of 0–100%. Concentrationwas measured immediately above the foam and also withinthe foam, but the number of measurements taken waslimited by the build-up of moisture in the sampling tube.PathologyA complete macroscopic necropsy was conducted todetermine pathological changes or damage to differentorgan systems, with particular attention paid to bleedingand foam or water in the airways and bleeding in brain,liver or kidneys. Microscopic analysis of brain and lungtissue were also conducted.ResultsThe pH-neutral CO2foam was generated with an expansionrate of approximately 300:1. Within approximately 30 s(range 24–40), the test box was filled completely with foam(see Figure 1). Birds were immersed in CO2foam withinapproximately 20 s (range 12–40). The CO2concentrationin the zone 10 cm above the foam ranged between 40–75%while, in the foam itself, levels of up to 78% were recorded.The latter measurements were affected by moisture suckedinto the measuring tube and cannot be taken as exact.BehaviourAttempts to escape such as jumping and wing flapping atthe onset of foam injection were observed in two of the sixanimals; in one instance there was one single action at thebeginning of the foaming process whilst in the second therewere two; immediately prior to the onset of foaming andagain at the point of submersion. Outwith these reactions,all the birds remained quiet and stationary in the test boxalthough all were visibly more watchful and alert. Prior tocomplete immersion in the foam, headshaking wasobserved in one bird and gasping in another two. Gaspingwas characterised by mild, deep breathing without bendingthe neck backwards. Directly after immersion, two birdsjumped up once. This strong movement could not be classedas a convulsion and was more akin to an attempt to escape.Forceful activity that could be classed as convulsions wereseen in five of the six birds at between 30 and 56 s after thestart of foaming. The convulsive movements (ie strong,uncontrolled leg and wing movements) were observed infour out of six birds, followed by wing flapping from anaverage of 60 s after the onset of foaming.Temperature and heart rateShortly before foam injection the average skin tempera-ture of the hens was 25.4°C and during foaming this roseto 27.4°C. The heart rate (Figure 2) was measured for© 2008 Universities Federation for Animal Welfare
  3. 3. On-farm killing of poultry with CO2-enriched foam 287three minutes prior to the onset of the foaming process.During this period all the birds showed a regular heart rateof approximately 300 bpm (range 270–370). Duringfoaming no major changes in heart rate were observeduntil the heart instantly ceased beating. This instantdecline in heart rate occurred at an average of twominutes (range 1.2–4.5) after the onset of foaming. Afterthis instantaneous drop some irregular phases of heartbeatwere observed prior to the cessation of any signal.PathologyMacroscopic post mortem observations revealed no abnor-malities on the exterior of the birds and no internal abnor-malities were observed in the thorax and abdomen,cardiovascular system, spleen, liver, gastrointestinal systemor central nervous system. Five out of the six birds hadtraces of saliva in the tracheae and, in one, moderate rednesswas observed in the lungs. These airway abnormalities wereclassed as minor to moderate changes and no foam or soapwere found in the lungs or airways. Liver and brainmicroscopy showed no abnormalities. All six animalsshowed evidence of bleeding in the tertiary bronchiole, witha number of others showing bleeding in the interstitial bron-chiole. Histological examination revealed two out of sixindividuals with alveolar bleeding.DiscussionBirds showed minimal fear behaviour during foamingalthough all birds displayed greater alertness during foamingcompared to prior to injection. A degree of headshaking andgasping prior to birds being covered with foam indicates aneffect of free CO2at the periphery of the foam.Animal Welfare 2008, 17: 285-288Figure 1View of chicken in test box, 20 s afterfoaming.Figure 2Heart rate (bpm) of one bird during thefoaming experiment. Heart rate wasmeasured and averaged over 10 s every30 s. Noise interference on the signaltrace meant that the bpm did not stabiliseon the x-axis. A: start measuring; B: startfoaming.
  4. 4. 288 Gerritzen and SparreyConvulsive movements, wing flapping and leg-shaking arealso seen during gassing with CO2(Gerritzen et al 2006a,2007) and were observed to occur at or just after loss ofposture and are therefore indicative of loss of consciousness.Based on this assumption, it can be concluded that loss ofconsciousness occurred within one minute of the onset offoaming. However, it must be noted that the moment of lossof consciousness was not directly measured in this pilot study.The acute drop in heart rate to zero or very close to zeroindicates an acute death of the animals. This point, inconjunction with no observed bleeding in brain tissue —which is indicative of asphyxia and hypercapnic hypoxia —makes it most likely that death arose for metabolic reasons;in this instance due to the high levels of CO2(N Stockhofepersonal communication 2007). The only pathologicalabnormalities observed were bleeding in the bronchiole andalveolar tissues. Taking these findings in the context ofhaving no previous studies with which to draw comparison,it is difficult to draw any conclusions on the cause of thisbleeding. However, bleeding such as this is also reported forCO2gassing experiments (Ryan 2006).The objective of this pilot study was to detect whether CO2-enriched high expansion foam has the potential to be anacceptable and efficient method for emergency killing ofpoultry. When we take into account behavioural parameters,measurements of heart rate and pathological data, it is ourconclusion that CO2foam is a potentially acceptable killingmethod for laying hens. Furthermore, the authors advise anexamination of this method on a larger scale in order toexplore the implications for animal welfare of physiological(EEG and ECG) measurements. It is also suggested that acomparison of different types of foam, different bubblesizes and different gases or gas mixtures, eg nitrogen (ABMRaj personal communication 2008) be carried out to createa bank of knowledge on this subject.ReferencesBenson E, Malone GW, Alphin RL, Dawson MD, Pope CRand van Wicken GL 2007 Foam-based mass emergency depop-ulation of floor-reared meat-type poultry operations. PoultryScience 86: 219-224Dawson MD, Benson ER, Malone GW, Alphin RL, EstevezI and van Wicken GL 2006 Evaluation of foam-based massdepopulation methodology for floor-reared meat-type poultryoperations. Applied Engineering in Agriculture 22(5): 787-794Gerritzen MA, Lambooij E, Reimert HA, Stegeman Aand Spruijt B 2004 On farm euthanasia of broiler chicken:effects of different gas mixtures on behavior and brain activity.Poultry Science 83: 1294-1301Gerritzen MA, Lambooij E, Reimert HGM, Spruijt BMand Stegeman A 2006a Susceptibility of ducks and turkeys tosevere hypercapnic hypoxia. Poultry Science 85: 1055-1061Gerritzen MA, Lambooij E, Stegeman A and Spruijt BM2006b Killing of poultry during the 2003 avian influenza epidemicin The Netherlands. The Veterinary Record 159: 39-42Gerritzen MA, Lambooij B, Reimert H, Stegeman A andSpruijt B 2007 A note on behaviour of poultry exposed toincreasing carbon dioxide concentrations. Applied Animal BehaviourScience 108: 179-185Kiezebrink H 2007 Method for the Sanitary Slaughter of an Animal.International Patent Application. WO 2007/021178 A1. WorldIntellectual Property Organisation: Geneva, SwitzerlandRyan J, Sheehan M, Wrigley K and Gaynor S 2006 Reporton the Real-Time Exercise of the ‘Whole house’ Carbon DioxideGassing Technique for the Humane Killing of Poultry in a DiseaseEmergency. State Veterinary Service, Department of Agricultureand Food: Ireland© 2008 Universities Federation for Animal Welfare